Ultra thin films having a thickness of less than 3 .mu.m, particularly less than 1 .mu.m, are required for the production of capacitors used in microelectronics. But, such films are difficult to produce on a large production scale.
Several processes for the production of ultra thin films have been described in the relevant literature. These processes generally utilize the following process steps: producing a thin film together with or on a base film, peeling the thin film off the base film, and then rolling up the thin film.
In British Patent Specification No. 1,190,698, the single films are joined together or adhered by pressure and/or heat. In this process, however, creases in the films are caused by slight thickness variations in the single films. These creases are formed repeatedly and are ironed into the film during the laminating process. The resulting creased thin films are useless for their intended purpose.
In U.S. Pat. Nos. 4,017,227 and 4,076,785, a device for casting two sheets next to each other and then joining those sheets before stretching in transverse direction is described. In this method, however, the supporting function of the base layer is missing and the splitting of the thin film is frequently observed.
In U.S. Pat. Nos. 4,708,905 and 4,756,064, coextruded laminated films, where the individual layers are made of different polymers, are stretched and then delaminated. Problems result from this process because each polymer has a different flow velocity and the velocities cannot be coordinated exactly. Regulating a uniform thickness profile across the film width creates the greatest problem, since allocating thickness distribution of the base film and the coating film is difficult. Additionally, the different polymer layers are subject to casual fluctuations during coextrusion.